Centrifuge with improved discharge assembly



27, 1958 M. M. KOENECKE ETAL $398,838

CENTRIFUGE WITH IMPROVED DISCHARGE ASSEMBLY 4 Sheets-Sheet 1 Filed Aug.18, 1966 CENTRIFUGE WITH IMPROVED DISCHARGE ASSEMBLY FIG. 3

Aug. 27, 1968 M. M. KOENECKE ETAL 3,398,888

D DISCHARGE ASSEMBLY CENTRIFUGE WITH IMPROVE 4 Sheets-Sheet 3 Filed Aug.18, 1966 Aug. 27, 1968 KOENECKE ETAL 3,398,888

CENTRIFUGE WITH IMPROVED DISCHARGE ASSEMBLY 4 Sheets-Sheet 4 Filed Aug.18, 1966 FIG. 7

United States Patent 0 ABSTRACT OF THE DISCLOSURE A centrifuge having abowl rotatably mounted in a housing. A plurality of expansionable andcontractable panels are mounted on the interior of the housing oplposite the solids discharge end. Pulsating air pressure is supplied tothe panels to break up and discharge solid cake material which normallywould stick to the housing.

This invention relates to a centrifuge for separation of solids fromliquid suspensions. More particularly the present invention relates to acentrifuge equipped with an improved assembly for the discharge ofsolids.

Commercial centrifuges have been in use for some time which embody arotating bowl and screw conveyer to separate a solid phase from a liquidsuspension by means of centrifugal force. These centrifuges arecommercially used where the solid particles have a higher density thandoes the liquid phase. Considerable difficulty has been encountered inoperation of the foregoing type centrifuges when used with solids havinga tendency to adhere to each other and to the discharge surfaces of thecentrifuge. Specifically a severe problem has been encountered inseparating solid thermoplastic particles from suspensions. Aparticularly acute problem has been encountered in separating polyvinylchloride particles made by the suspension process from the suspensionliquid. In one commercial centrifuge installation it was found that itwas necessary to shut down the centrifuge for manual cleaning afteroperating periods as short as two hours.

One prior art method has attempted to prevent the solid material fromsticking to the area around the solids discharge end of the centrifugeby providing a single band of vulcanized rubber around the area (see US.Patent 2,324,933). In this centrifuge it was necessary to adhesivelyattach the edges of the single elastic strip to the housing to permitair pressure to be applied to the space between the centrifuge and theelastic band. The seal frequently leaked causing severe maintenanceproblems with this device. Further, the rubber strip was severely wornin certain localized areas in a very short time which necessitatedchanging the entire rubber strip. The centrifuge of the presentinvention overcomes the objectionable features of the foregoing priorart centrifuge.

An object of the present invention is to provide a centrifuge having animproved assembly for the discharge of the solid phase.

Another object of the present invention is to provide a centrifuge whichcan operate at sustained intervals without the necessity of shuttingdown for cleaning.

An additional object of the present invention is to provide a centrifugehaving means for periodically cleaning the surfaces in the solidsdischarge area.

A further object of the present invention is the provision of acentrifuge having means to permit ready replacement of localized surfaceareas which are subject to wear from abrasive solid particles.

3,398,888 Patented Aug. 27, 1968 The foregoing, and other aims, objectsand advantages of invention as may appear hereinafter are realized in acentrifuge having a housing and a bowl rotatably mounted in the housing.The bowl is provided with means for discharging solids at one endthereof. A screw conveyer is rotatably mounted inside the bowl. Aplurality of expansionable members are provided within the housing inthe solids discharge end of the centrifuge to break up the cake whichnormally forms at this end of the centrifuge.

In the drawings:

FIG. 1 is an elevational view of the centrifuge of the present inventionhaving portions thereof broken away to show the internal structure;

FIG. 2 is a cross sectional view taken along the line 22 of FIGURE 1;

FIG. 3 is a longitudinal sectional view taken along line 3-3 of FIGURE1;

FIG. 4 is an exploded view in perspective of the solids collectionassembly utilized in the centrifuge of the present invention.

FIG. 5 is an elevational perspective view of one embodiment of theexpansionable members utilized in present invention;

FIG. 6 is an elevational perspective view of a second embodiment of theexpansionable members utilized in the present invention; and

FIG. 7 is a schematic diagram of the air supply system for theexpansionable members.

Referring now to the drawings, particularly to FIG- UREE l and 2thereof, the centrifuge includes a housing, designated generally by thenumeral 10, and a base 11 which provides support for the rotatable bowl12 positioned within the housing. A hollow, rotatable screw conveyer 13is provided within the bowl 12 and is suspended independently of thebowl by means of a rearward solid shaft 14 and forward hollow shaft 15.Shaft 15 is supported by bearing assembly 16 which is received in therecess 17 provided in the forward end of the interior of bowl 12. Bowl12 is rotatably supported at its forward end by means of hollow shaft 18which is suported in bearing block assembly 19 which rests on a portionof the base 11. The rear end of the bowl 12 is supported by hollow shaft24) which is in turn supported by bearing block assembly 21 resting onbase 11. The rearward shaft 14 of the screw conveyer is supported bymeans of a bearing assembly (not shown) within the drive gear assembly22.

Axial feed tube 23 is mounted on support bracket 24 and projects throughthe hollow forward shaft 15 to the hollow interior of the screw conveyor13. Slurry flows from the opening 25 provided in the end of feed tube 23through ports 26 provided in the wall of hollow screw conveyor 13.Pulley 27 is connected to hollow shaft 18 and rotates the bowl 12 in acounter-clockwise direction through V- belts and a drive motor (notshown). Screw conveyor 13 is rotated 'by means of drive shaft 14 throughdrive gear assembly 22 by means of a motor (not shown). The screwconveyor 13 and the rotating bowl 12 are rotated on their longitudinalaxis in a clockwise direction as viewed from the end of the centrifugeequipped with pulley 27. Hollow screw conveyor 13 rotates in the samedirection but at a lower r.p.m. than does the bowl 12 thereby movingsedimented solids by means of the flight screw 28 affixed to the outersurface of the screw conveyor 13. The centrifugal force imparted to theslurry separates the slurry into solid and liquid phases. Solids aresedi-rnented against the interior surface of the bowl 12 and propelledby flight screw 28 to the beach area 29 of the bowl 12 and then outthrough solids discharge ports 30 provided in one end of centrifuge bowl12. The clarified liquid flows through ports 31 provided in the rearwardend of the bowl 12. The discharged liquid then flows through liquiddischarge pipe 32 to a drain or stor age vessel.

g The solids discharge end of the centrifuge is provided with acollector area defined by the forward end wall 33 of the housing 10together with a bafiie plate 34 surrounding the bowl 12 and attached tothe interior wall of housing 10.

Within the collector area a solid discharge assembly designatedgenerally by the number 35, is provided. As can be seenrnore clearlythan FIGURES 2, 3 and 4, the solid discharge assembly 35 includes aplurality of interconnected support panels 36 which form an inverted U-shaped structure within the solids collector area. The forward wallmember 37 is attached to to one side of the interconnected supportpanels 36 by means of bolts 38 and nuts 39;. A rearward wall membernumber 40 is attached to the opposite edges of interconnected supportpanels 36 by bolts 38 and nuts 39. Two rows of expansionable panels,designated generally by number 41, are attached to support panels 36 bymeans of bolts 42 as shown in FIG. 4.

As can be seen more clearly in FIGURE. 3, the expansionable panels 41have an elastic covering 43. An air space 44 is provided within eachpanel 41. A nipple 45 connects the air space 44 to a source ofcompressed air conveyed to each of the panels by means of tubing 46. Theelastic covering 43 may be of any suitable mate-rial possessing theability to expand and contract under the influence of compressed air.Among the suitable materials from which the elastic covering 43 may befabri cated are the synthetic rubbers. A preferred material for elasticcovering 43 is sheet polyurethane. This material has been foundeminently suitable in that it is highly resistant to the abrasive actionof hard solid particles. If desired the elastic covering 43 may befabricated from thin, flexible panels of stainless steel or othersuitable metal.

Referring now to FIGURE it can be seen that the expansionable panels 41may be individual side-by-side mounted panels. An alternate embodimentis shown in FIGURE 6 wherein a series of single expansionable panels 41amay be utilized with each individual panel covering the width of thesurface of the support panel 36.

The interior surface of forward wall member 37 is covered with a coating47 of a material which provides a non-stick surface which resistsbuild-up of solid materials. Rearward wall member nu-mbef 40 has asimilar coating 47 provided on its interior wall as can be seen in FIG-URE 1. One material which has been found suitable for the non-stickcoating 47 is polytetrafluoroethylene (Teflon) which may be applied inthe form of an ladhesively attached sheet, or may be sintered onto thewalls by means of conventional sintering techniques. If desired theforward and rearward Wall members may be covered with a plurality ofexpansionable panels 41 in place of the non-sticking coating 47.

Referring now to FIGURES 3 and 7 compressed air is applied to the airspace 44 within each expansionable panel by means of interconnectingtubing 46. High pressure compressed air is supplied through pipe 48 tofilter 49, then to a pressure regulator 50, and then to an electricalpressure sequence controller, designated generally by the number 51. Airfrom the sequence controller 51 is carried by pipe number 52 throughexhaust valve number 53. Relief valve number 54 is connected to theexhaust valve 53 and to the sequence controller by a separate line.Tubing 46 conducts the low pressure air to each expansionable panelcarried by the support panels 36 through a network of interconnectedtubing runs as shown in FIGURE 7.

As seen in FIGURES 1 through 4 the solid material is discharged throughports 39 in the direction of the arrows where thesolid material thenstrikes the solids discharge assembly which surrounds the solidsdischarge end of the centrifuge. The major quantity of solids are thrownagainst the series of expansionable panels 41 where a gradual build-upof densely packed partcles occurs. After an interval of time determinedby the setting of sequence controller 51 air pressure is supplied toeach of the panels 41 to expand the elastic covering which results inbreaking off the accumulated solid layer from surface of each of thepanels 41. The sequence controller then vents the air through exhaustvalve 53. The panels 41 are alternately expanded and contracted on afixed schedule when the centrifuge is operating. A pulsating time of /2to 1 second has been found satisfactory for discharging polyvinylchloride particles. This broken caked material then drops into the solidcollection system through the opening 55 in the bottom of thecentrifuge. Relatively small quantities of solid materials are thrownagainst the forward wall 37 and rearward wall 40. The non-stick coating47 on each of these walls prevents any substantial quantity of the solidmaterial from adhering to the end walls of the discharge assembly. Ifdesired one or more additional low pressure air supply lines 46 can berun from the sequence controller and connected to alternate panels.These additional supply lines are connected to a separate timer which isset to provide a pulsation cycle that is opposite to that on which theprimary supply operates. This system is sometimes more effective inbreaking up the caked material than is the simultaneous pulse systemdescribed hereinbefore.

The discharge assembly used in the centrifuge of the present inventionis a decided improvement over a vibrating solids discharge ring whichhad been used with some centrifuges heretofore. As mentionedhereinbefore, sometimes a single band of elastic material, usuallyvulcanized rubber, has been used to attempt to break up the cake ofsolid particles in the solids discharge area of the centrifuge. Problemswere encountered in that bonding of the elastic strip was difficult tosecure and also the short life of the rubber strip required frequentshutdown of the centrifuge for replacement. Furthermore, the strip wassubject to the high abrasion in localized areas and it would fail beforea. reasonable life expectancy was achieved. The present centrifuge byutilizing a plurality of individual expansionable panels permits thereplacement of those panels which are subjected to erosive forceswithout the necessity of renewing the entire surface that is exposed tothe abrasive solids. Continuous openating periods as long as aboutfourteen days to about twentyeight days have been achieved using thepresent lCfil'ltIlfuge for separating polyvinyl chloride from a watersuspension. Heretofore the maximum operating time for a centrifugewithout the pulsating panels in PVC service was about two hours.

The foregoing disclosure and description of the invention isillustrative and explanatory thereof. Other modifications will beapparent to those skilled in the art. Therefore the present invention isto be limited only by the scope of the appended claims.

We claim:

1. A centrifuge comprising: a housing; a bowl rotatably mounted in saidhousing, said bowl having means for dis- 4. The centrifuge of claim 3wherein said last mentioned means includes compressed air.

5. The centrifuge of claim 4 including means for simultaneous-lyexpanding alternate panels and contracting intermediate panels.

6. The centrifuge of claim 1 wherein said housing is provided with acoating of material to render the surface non-sticking in the areaadjacent said plurality of expansionable members.

References Cited UNITED STATES PATENTS McGlaughlin.

Jones.

Abbott 233-46 XR Borig 233-22 Meryman et al. 233-27 HENRY T. KLINKSIEK,Primary Examiner.

